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Ann. Geophys., 36, 139-147, 2018
https://doi.org/10.5194/angeo-36-139-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Regular paper
25 Jan 2018
Latitude-dependent delay in the responses of the equatorial electrojet and Sq currents to X-class solar flares
Paulo A. B. Nogueira1, Mangalathayil A. Abdu2, Jonas R. Souza2, Clezio M. Denardini2,3, Paulo F. Barbosa Neto2,3, João P. Serra de Souza da Costa1, and Ana P. M. Silva1 1Federal Institute of Education, Science and Technology of São Paulo, Jacareí, São Paulo, Brazil
2Divisão de Aeronomia, Instituto Nacional de Pesquisas Espaciais, São José dos Campos, 12227-010, São Paulo, Brazil
3Embrace Space Weather Program, Instituto Nacional de Pesquisas Espaciais, São José dos Campos, 12227-010, São Paulo, Brazil
Abstract. We have analyzed low-latitude ionospheric current responses to two intense (X-class) solar flares that occurred on 13 May 2013 and 11 March 2015. Sudden intensifications, in response to solar flare radiation impulses, in the Sq and equatorial electrojet (EEJ) currents, as detected by magnetometers over equatorial and low-latitude sites in South America, are studied. In particular we show for the first time that a 5 to 8 min time delay is present in the peak effect in the EEJ, with respect that of Sq current outside the magnetic equator, in response to the flare radiation enhancement. The Sq current intensification peaks close to the flare X-ray peak, while the EEJ peak occurs 5 to 8 min later. We have used the Sheffield University Plasmasphere-Ionosphere Model at National Institute for Space Research (SUPIM-INPE) to simulate the E-region conductivity enhancement as caused by the flare enhanced solar extreme ultraviolet (EUV) and soft X-rays flux. We propose that the flare-induced enhancement in neutral wind occurring with a time delay (with respect to the flare radiation) could be responsible for a delayed zonal electric field disturbance driving the EEJ, in which the Cowling conductivity offers enhanced sensitivity to the driving zonal electric field.

Citation: Nogueira, P. A. B., Abdu, M. A., Souza, J. R., Denardini, C. M., Barbosa Neto, P. F., Serra de Souza da Costa, J. P., and Silva, A. P. M.: Latitude-dependent delay in the responses of the equatorial electrojet and Sq currents to X-class solar flares, Ann. Geophys., 36, 139-147, https://doi.org/10.5194/angeo-36-139-2018, 2018.
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Short summary
We have analyzed the low-latitude ionospheric responses to solar flares. In particular we show for the first time that 5 to 8 min of time delay is present in the peak effect in the EEJ, with respect that of Sq current outside the magnetic equator, in response to the flare radiation enhancement. We propose that the flare induced enhancement in neutral wind occurring with a time delay could be responsible for a delayed zonal electric field disturbance driving the EEJ.
We have analyzed the low-latitude ionospheric responses to solar flares. In particular we show...
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